1. Field of the Invention
The present invention pertains to wireless telecommunications, and particularly to the sharing of antennas by plural radio base station nodes.
2. Related Art and other Considerations
In a typical cellular radio system, mobile user equipment units (UEs) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a radio base station node. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The radio base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several radio base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
One example of a radio access network is the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN). The UMTS is a third generation system which in some respects builds upon the radio access technology known as Global System for Mobile communications (GSM) developed in Europe. UTRAN is essentially a radio access network providing wideband code division multiple access (WCDMA) to user equipment units (UEs). The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM-based radio access network technologies. In the UTRAN, a radio base station node is also referred to as a B-node or node B. As used herein, the terms “base station”, “radio base station”, or the like shall be understood to encompass all types of radio base station nodes, including the B-node of the UTRAN.
A radio base station might employ a tower mounted amplifier (“TMA”). Tower mounted amplifiers (TMAs) are generally of three different types. A first and basic type of TMA is for receiving only, and has a receiver (RX) input coming from a receive antenna and a receiver (RX) output going to a feeder. A second type is a duplex TMA (denoted dTMA) which connects to a combined transmit and receive antenna and is connected to a transmit (TX) feeder and a receiver (RX) feeder. A third type is a dual duplex TMA (denoted ddTMA) which is connected to a combined transmit and receive antenna and a combined feeder (used both for receiving and transmitting).
It can occur that a radio access network operator may desire to situate a new radio base station on a site where another radio base station operates. The new radio base station may be of the same or different telecommunications network technology (e.g., a same or different standard) than the existing/older radio base station. For example, the new radio base station may be a node-B which functions in conjunction with a UTRAN, while the co-located older radio base station may be a node of a GSM network.
Perhaps the most straightforward approach for co-locating two radio base stations is to put up new antennas and feeders at the same site for the new radio base station. While this may, in some instances, be an optimum solution, there is considerable cost involved in climbing the mast to install a new antenna. Moreover, the weight of the new equipment may be too great for the mast, or there might be some other problem with allowance. In some situations, The co-location of the new radio base station with the older radio base station achieves some efficiencies and economies, particularly in the sharing of antennae and feeders for the antennae.
One of several prior art methods could be utilized for enabling two radio base stations to share receiver antennas on the same frequency band. A sharing of transmit antennas results in a power loss of approximately 3.5 decibels (dB). If antenna sharing is structured incorrectly, there may be undesirable results such as loss of sensitivity, an inaccurate receiver level, or considerably more intermodulation. Moreover, inept antenna sharing may spoil the alarm handling at the base station. In this regard, a tower mounted antenna (TMA) sends its alarms through the DC-supply current (e.g., if the current is outside prescribed limits, an alarm occurs). Service personnel typically have to visit a base station site when an alarm occurs.
A first possible method whereby two radio base stations can share antenna is sometimes referred to as the “tower mounted amplifier (TMA) on-ground solution”. As its name implies, with the tower mounted amplifier (TMA) on-ground solution a tower mounted amplifier (TMA) is situated on the ground, and connected much in the example manner illustrated in FIG. 1. In the tower mounted amplifier (TMA) on-ground solution, a receiver output port of the tower mounted amplifier (TMA) is connected to an input port of a splitter, with output ports of the splitter being connected to the receiver bandpass filters, and ultimately to the low noise amplifiers (LNAs), of the two base stations (e.g., of a main radio base station and a co-sited radio base station). The first of the two radio base stations has its bandpass filter and LNAs housed in a first radio base station cabinet, while the second of the two radio base stations has its bandpass filter and LNAs housed in a second radio base station cabinet. The splitter, feeder, TMA, and antenna are considered external equipment since they are outside of the cabinets. Unfortunately, if a customer (network operator) purchases a tower mounted amplifier (TMA), installation of such a tower mounted amplifier (TMA) will influence the overall mean time between failure (MTBF), which is a statistical value of how often a fault occurs. Moreover, installation of a tower mounted amplifier (TMA) involves adding external equipment outside the cabinet, which could present spatial and/or environmental issues (particularly in the case of an outdoor radio base station.
A second possible method is known as the “raw split”. The raw split sharing method resembles the tower mounted amplifier (TMA) on-ground solution, but does not have a tower mounted amplifier (TMA). However, in the raw split method even if the antenna sharing is performed correctly, there is much sensitivity loss (3.5 dB) since the overall noise figure is increased.
A third possible method is a technique of using the old radio base station as a “master” and to feed the receiver of the old radio base station to the new radio base station. Yet this technique has the disadvantage of necessitating considerable work with respect to the old radio base station.
There are other possible methods which involve (in various ways) connecting the receive path of the new radio base station to the old radio base station but keeping the overall gain of 0 dB (in order to keep the same receive level to the transceiver [TRX].
What is needed, therefore, and an object of the present invention, is a technique for allowing co-located radio base stations to share antenna without undesirable operational effects.